Power supplies are used in a variety of electronic products including automotive, aviation, telecommunications, consumer electronics, portable electronic products such as laptop computers, personal digital assistants, pagers, cellular phones, etc. Generally power supplies are categorized as linear power supplies or switching power supplies. Linear power supplies are less complex than switching power supplies; however, they are typically larger, heavier, and less efficient than switching power supplies. FIG. 1 is a circuit schematic of a typical buck switching power supply 10 that includes a modulator 12, a switch control circuit 14, switching power transistors 16 and 18, diodes 17 and 19, and an error amplifier 20. Switching power transistors 16 and 18 deliver power to a load 22 through inductors 24 and 26, respectively. In operation, switch control circuit 14 generates switching signals that turn transistors 16 and 18 on and off to form output signals having a variable duty cycle that are transmitted through inductors 24 and 26 to a load 22 to generate the desired output voltage, VOUT.
Switching power supplies are used to provide power to processors such as central processing units and graphical processing units, thus it is desirable that they be able to increase or decrease their output voltages with fast slew rates. Switching power supplies may include Adaptive Voltage Positioning (“AVP”) control schemes to further enhance the thermal performance of the switching power supplies and their loads. In switching power supplies that use AVP control, the output voltage is designed to droop linearly with increasing current and typically a droop amplifier is used for measuring the output current and controlling the output droop voltage. The slewing of the output in combination with the AVP control scheme slows the rate at which the output voltage changes because of the output capacitance charge or discharge current that is present in a droop amplifier. The droop signal causes the output voltage to position itself either lower or higher for charging or discharging the output when the voltage regulator is being changed to a higher or lower output voltage, respectively, thereby slowing the output response. One technique for increasing the output voltage slew rate in switching power supplies that use AVP control techniques is to include an error signal that compensates for the droop signal that slows or decreases the output slew rate. A drawback with this approach to increasing the slew rate is that including the error signal fails to address the root cause for the slowing of slew rate and it increases the complexity and area of the circuit design.
Accordingly, it would be advantageous to have a method and circuit for increasing the slew rate of a power supply or removing the slowing effect that the AVP droop signal has on the output slew rate. In addition, it is desirable for the method and circuit to be cost and time efficient to implement.